Koi wo Suru DNA +

A limited edition special book which includes these stories:
1) Koi wo Suru Shokubutsu
Sports stars, Hiyama and Mizuno, find themselves caught up in something bigger than they first imagined when they go out to find out whether or not their fathers are really gay.
2) Koi wo Suru DNA
Hiyama and Mizuno are back for more trouble!
3) Koi wo Suru Baby Leaf
4) Koi wo Suru DNA+
Hiyama Papa and Mizuno Papa reminisce about a passionate meeting in their youth.
(Source: MangaUpdates)